Effect of trans-ligand on properties of nitric oxide motif in nitrosylcobinamide

Abstract

Nitrosylcobinamide (NOCbi) is a tight complex between Co(II)-form of cobinamide, a nucleotide-free analog of cobalamin (vitamin B12), and nitric oxide (NO). Here, we report that NOCbi exhibits high resistance toward aerobic oxidation in comparison with nitrosylcobalamin. NOCbi slowly degrades in the presence of hydrogen peroxide and undergoes a more rapid oxidation by H2O2/peroxidase (viz. horseradish or lactoperoxidase) mixture to nitrocobinamide. Aerobic oxidation of NOCbi is accelerated by addition of ligands (i.e., imidazole, cyanide, and others). The mechanism of NOCbi oxidation in the presence of these ligands can be represented by two parallel routes: the axial ligand binding on NOCbi (i) results in the elongation of Co(II)-NO bond, leading to acceleration of NO-dissociation and further NO reaction with O2 to give NO2, and Cbi(II) oxidation by NO2, and (ii) facilitates reaction of the NO-motif with O2 to give peroxynitrite intermediate decomposing to nitrite and dioxygen. Decrease in aerobic stability of NOCbi may occur in vivo upon reaction with side chains of extracellular proteins, that was indicated using bovine serum albumin.